Single-site Group 3 and Lanthanide

2 Single-site Group 3 and Lanthanide Series Metallocene Catalysts 

The polymerisation proceeds quite slowly, presumably owing to the inactivity of the formally d° 16-electron yttrium species of the dimeric catalyst. A formally d° 14-electron monomeric hydride or alkyl derivative is probably required for olefin polymerisation [187], 

Dimeric homochirotopic [rac.-Me2Si(Me3Si, t-BuCp)2YH]2 is the first singlecomponent isospecific catalyst it is suitable to study the subtle steric factors that govern the remarkably high stereospecificities exhibited in the polymerisation of a-olefins by this and related two-component class III catalysts of C2 symmetry based on group 4 metallocenes. 

Cationic [ZrBz3]+ species are capable of polymerising oc-olefins such as propylene, 1-butene and 1-pentene at elevated temperature. It is worth emphasising that the non-metallocene [Zr(CH2Ph)3] + [PhCH2B(C6F5)3] catalyst, which is a cationic arene zirconium complex [189], is capable, at least partially, of isospecific a-olefin polymerisation at relatively high temperature [162,189,190], 

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